Production of cellulose esters



Patented Sept. 2l, i943 rRonUorroN or ententes-seepage George W. Seymourvand lanchef. liihite,

Dumberland,- Mld.,Y assgno'rs to-v Celanese Corporation otArneric'a, a corporation.cfDelawai-e f Ndnrawing. Application April 9,1941, Serial No. 387,606 y n :n claims. (e1. estreo) This invention relates to yimprovernents, the production of cellulose esters, and is more .particularly concerned with the production ofv cellulose acetate or other cellulose esters particu-y iarlylower fatty acid esters of cellulose.

This. application is a continuation-impart 4of U. S; application S. No.. 328,803, illed'April 1Q, i940, which in turn a continuation in part or" U. S. applications S. Nos; 251,764, filed March 14, 1939, 24,127led March 25 1939, and 277,028 iiled June 2, 193,9. y

In 'the manufacture of cellulose acetate, the cellulosa with or Without a pretreatment fwith organic acids or organic acids containing a little sulphuric acid, is customarily acetylatedzwith a medium containing acetic anhydriddacetic acid and sulphuric acid, e, g., in a proportion of some 9-15% on the Weight of' the cellulose. Sonie vof this sulphurlc acid may have been introduced in a pretreatment designed to make. the cellulose more reactive. When the acetylation is cornplete, water is stired into the mixture, and the.` whole allowed to stand until a sample shows that the desired acetone-solubility has been reached. During this standing period, or ripening period as it is usually called, not only are acetyl groups split ci?, but in addition combined sulphuric'acid. is split ofi. With a View to obtaining cellulose acetates of a sufciently high Viscosity for the production of filaments and for the production strong lrns and sheets', the. customary com-l merci-al practice is not to allow the temperature during the acetylation `to rise above a certain Value, for example about 35C., and also to conduct the ripening at substantially atmospheric temperature, for example at a temperature-.of 22e-28 C. In this Way, cellulose acetates' hai/inarv a viscosity of lil-20 ormore may he' produced, these units being a measure of the rate of iioWv of a. 6% solution of cellulose acetate in acetone, taking the rate offiow ofglycerine as 1G51. G'fe'norally if the temperature during the acetylation' is allowed to go up say to 58 C.. or 6d" C., as in the early Miles process for producing an aceto-ne? soluble cellulose acetate, or if the mixture is heated during ripening, a lowV viscosity cellulose acetate resuits, suitable, for. example, for lacquer purposes. 'When the desired/acetyl value has been reached in the ripening operation, the cel-r lulose acetate is precipitated and Washed, and is to a stabilizing treatment, usual#l in suspension in a very dilute sul-"f phuric acid with the object of 'still further'. reducthe?` subjected ly by heating it ing its content oi combined sulphurcacid.

n,v the production 'ofU the Vcellulose acetate.v

. total period of. acetylation land` ripeningv Whilev vstill obtaining a `cellulose.acetate suitablefor the for the purpose of 'forming filaments.. rlmsj and sheets as described above,I the acetylation itself,y may tale some 4-8hoursandthe ripening Vfrom' 20`to` 451er 50 hours. 'One of theobjects of the, presentinvention is fto reduce substantially the manufacture. `oilan'ients .and sti'ong"-fi,lrns`, sheets` and the like'both from 'the point of View of the Viscosity 1 and clarity of the Lfcellulcse Yacetate` Further, itis possible by inean of the present ,in-l velticnto obtainmasa result he ripeningoper'- ation `cellulose a'cetates. irai/irreV a` substantially" reduced content of coinbnd sulphuiic acidi` yt'has been found i'fgiafte'r yan'.acetil-lation asl 'described abovapthe 'suipnuric acidconten't 0i the' acetyiatiori medi-um is attested to a cfe'rf` tainrange of values,r the ripening' maybe oonducted 'at elevated temperatures Without producing serious degradation offtlief'zellu-lose, sothat' the? acetone-soluble product 'still a'- suciently high viscosity ana clarity tvo-produce goed anfments andstrong'vcleafr lfrnsand sheets. Euriiier, it has been; foune' that Wit-riuiis're'ngeof Values of SulphurC/"acid cntlflft, `even .if-thA ripening is enseres at temperatures which are only' slightly? above Yiiorinal' ripeningfternperatures, for exa'iiipieiisitte eenoueba ai, tempera-f tures of 304 C.; substantial aduantage accrues .in that the product has a lower contentA than usual of combined sulphuriacid 'at the end of the ripening treatin-ent.'- -Tlisrange of' Values of" sulphuric acid is soinewlialt"lower` than themost advantageous proportions of sulphuric ,acidv for use in tlz'er acetylationitslf, andI consequently' there may be' added attlfie' ogi1-ln-i'ngy of the ripenin' treatrnent,'either beforeo-r after the Water or together lwith the Water for ripening, 'a proportion of magnesium' acetate', mag'nesumcar# bonate or the likesuch' that the sulphuric acid contentis adjusted' to thed'esred value. l

l Tnem'st advantageous rang-eef values -for ripening at temperatures up to-65 C; is about k acetylatiorifis conducted `with i of sulphuric acid based on the cellulose, and-if 4 8 or; 9%' of free sulphuric .scia based 'onine weight of the cellulose used starting xfiaterial'.`

Withhigher temperatures, yfor example 'w-90 C.,

still lower` .values for the free sulphuric acid' the ripening isV to be conducted at about 50-60 C., yit is most advantageous to addsuiicient mag-'- nesium acetate'or carbonate .to neutralize' about one-thirdfto twothirdsrof the i sulphuric vacid present. Fertige purposes 'of this specification" it produced by the ripening treatment have a revduced content of combined sulphuric acid. This content of combined sulphuric acid may be so low that stabilization is unnecessary, but the necessity or otherwise for stabilization depends inter alia upon the temperature used for the ripening and upon the amount of water added for ripening. Moreover, the amount of water to' be1 added to the ripening bath for ripening purposes" depends, in general, upon the content of free acid in the ripening bath as well as upon the temperature used for ripening. vFor example, whenthe ripening Vis conducted with an` amount of sulphuric acid equal to from 4 to 8% of the weight of the cellulose originally employed at a temperature ofabout 35 C., 'the amount 'of'water used for ripening may advantageously'be from. 6 to 20%, and preferably 18 toV 19% ,i based on the .weight of theoriginalfcellulose. Whenfcond'ucting theripening with an amount of sulphuric acidequal to 9% f the weightof the original cellulose at atenperature of about `30" C. the amount of water used `for ripening should not exceed about of the original weight ofthe cellulose. With an amountlof free sulphuric acid of about'5% at the same temperature, the amount `of water used should not exceed about of the original Weight of .theV cellulose. In all cases in this speci-v cation the amounts of water used for ripening exclude thed amount-of water necessarily added for the purpose of destroying or killing the acetic anhydride left over at the end of the acetylation. When using higher temperatures yfor ripening, larger amounts of water mayg be employed. fFor example,with about 5% free sulphuric acid inV the ripening bath at a temperature of 40 C., the amountsof `water'used f or ripeningrnay reach 40%, while still' higher valuesmay be used with increasing temperature, for 'example anV amount upto 50%'at 60 C. i 1- i With a View vto producing,-` asa' result of the ripening treatmentcellulose acetates-ofvery low sulphuric acid Acontent,wthe water for ripening may be added kin two stages, that added at the rst stagebeing allowed toact for' some time, for example 2-4 hours or more,` and the water then added forA the second stage ripening. When ripening is conducted by this method, quite large amounts of water basedaon the original cellulose may be added. For example; with' a free sulphuric acid contentof about 5% on the original weight of the cellulose, and when conducting the ripening at say 60 C., an amount of'water based on the'- original cotton of50% may be added in theY iirststage, and the ripening continued' for some'4` hoursfand then; afurther quantity of water equal to as rmuch as 100% or more of the original weight ofthe cotton, mayfbe added and'this' allowed to act until the 'desired acetyl value is producedr, 5f

iTh'e Water for ripening may, where suitable, be added 'as such or may be added in the form of a dilute solution of acetic acid, it 'being merely necessary tol have it stirredin without producing any'substantial precipitation'of the cellulose ace- Atate or zinc oxide.

are still obtainable.

tate. The magnesium acetate, carbonate or the like may be added together with the water for ripening, particularly if this is added in the form of a dilute solution of acetic acid, or it may be added separately, e. g., in solution in glacial acetic acid. Other neutralizing agents may be used, though it is foundthat magnesium compounds are best. Other neutralizing agents in clude calcium acetate or carbonate and zinc ace- Alkali metal compounds do not givengood results.

Since the ripening treatment according to the L present invention results in the cellulose acetates having a lower content than usual of combined sulphuric acid at the end of the ripening treatment, Vthe invention is eminently suitable for the production of cellulose acetates of high acetyl content, particularly acetyl contents of .S6-57% or, more', calculated as acetic acid. Such acetates have been difficult to prepare according to the knownmethods of the art because when ripening is conducted normally, when the acetyl value has fallen to a value of 57% or even 56%, the sulphuric acid content is st ill too high for satisfactory precipitation and subsequent stabilization. By a careful adjustmentof the amount of free sulphuric acid, amount of water added for ripening and temperature of ripening, it is even possible to produce by the present invention cellulose acetates of high acetyl content which 'have such a low content of combined sulphuric acid that they do not require stabilization.

The water for ripening and the magnesium acetate, carbcnateor the like, are thoroughly mixed with the acetylation solution at the end of ,the acetylation, for example in a Werner- Pfleiderer. If desired, the agitation by means of the Werner-P-leidereror other mixing apparatus may be continued throughout the ripening treatment, particularly if the ripening treatment is conducted at high temperatures, for example at 50-65" C., for short periods.

In'working the present invention, the cellulose may, for example, be pretreated with acetic acid or formic acid, which may be present in a small amount, for example 20-50% on the weight of the cellulose, or in much larger quantities, for example 200% or even` 300% on the weight ofthe cellulose, and which may contain a small quantity` of sulphuric acid, for instance l/2-1 or 2% on the weight of the cellulose. The pretreatment is preferably allowed to go on for some hours, for example over-night, though much shorter periods may be used when sulphuric acid is `present, and the pretreated cellulose is then treated with acetic anhydride and sulphuric acid in the appropriate amount to bring about acetylation.

The temperature during the acetylation is preferably maintained at a fairly low figure, and forthis purpose the acetic anhydride and any acetic acid mixed therewith may be pre-cooled before introduction of the cellulose. However,

peak temperatures of 35 C. or even as high as 40 or 45' C. may be used in the process cf the pres ent invention, since by combining such an acetylation process with the special ripening treatment'of the present invention, good viscosities After the acetylation is complete, the ripening is conducted as already described. i

In operating the ripening treatment of the present invention at elevated temperatures, for example 5065 C., the ripening `time may be aeaazec goed clarity. o f teuer s ulpliurie acid. contentar@ reduced from the. hiehsgiirectei .Qrfil hours down to. 5 hours, 3 hours. 2; hour-eier. eilen less..4 depending on the particular temeeraiure emnloyeddunne4 the rineniiae endeten the amount ei ire., sulpiiurie a; d.: elieserlt.v decine tite tiren-idee consequence. the ripening may be conducted; continuous. process., the mixture being allowed to travel slowly througlgra suitable conduit, maintained at .the desiredtemperature and of sucli a length that-the epeed of Dasaaeeief' the mixture therethrough can be adjusted toy eive the. required time of treatment. Suele a conduit may be charged at one eed in .the acetylation room. and may. discharge. its` con. tents directly into. a preeinitatoe.. The. invention is V'particuler1.5 addressed toi the acetylation `oi cellulose sulphurie acid as. catalystsflowever., phespherica'eid may' be used in. ai similar Way. or mixtures loiniiosphorio acid and sulphurie acid., though the hestresultsare obtained. with -suliihurie acid alone. and' without the radiales. of any .other 'minerai acids. either' during the acetylation or during the ripening.I a similarway. other .cellulose esters. may be pre ated-fer example tiieLeelluloseestersl cintopicnic., butyric or 'similar acids. or. mixed.' esteis.. forV tatebutyate and the like.. .The following, examples' illustrate the; inver1. tion but do .not liinitit iu. anyway f Estefania .1? A100 Iparte or cotton are acetylatedf withA a mixtureco'ngprjising 375 par-ts ofv aceticacid. 215 paitso' acetic anhydride and 14 parts of s ulplauieie acid', the peak temperature being of .theV order-of 35i-40C; There is then stilired 'into the mixture an amount of water' suoient toi destroy the excess acetic anhydride, and: in` additionan amount enit/iat to l30% of' the original weight of thev cotton, together. with suine-ientmaenesium carbonate to combine with 9` parte. of the sul"- phuric acid present.' Theripening is theneected example cellulose acetate-Propionate. aee.-`

-A quicker ripeningy may be eiected byneutralizing all but 4% of the sulphuric acid. Otherwise-the.- eonditions are as: stated. in Example III- Tl-ie time of ripening in. t.. caseis reduced to t1a e .erderwoff 3l/endure: to obtain a product oi acetyl value fiedaea,

" 7 Ezccmple'V" 100.5 parts ci cotton are acetylated with an.

acetylatinfg'inixture comprising. 37.1A parts of aoetieaeid., 2 @parte of acetieanhydride and 14.7 parts otlizQi; `or a period of 1.5. hours. during whiclna. peak temperature of 42"- C. is. allowed to occur. There is,t hen added; just su'icient Water toreaot with any residual acetic anhydride in order to convert the same toacetic acid. The. ripenineis eiected by adding to. the acetylationA mixture stirring,- suiileieut magnesium eartionate. to neutraliaealljbut. parts vof the. suie' phuric acid (Sil-partsY of magnesium carbonate, analyzing 449.7%.'Mg0). and 1.8,.2 parts of water, and stirring the. mixture.

- Example VI.'v Acetylationqis- Conducted; as. in ,I5 and.

tnewater for ripening is, 48.70 'on t. Weight of thecottcn and the'. magnesium caldieuateA is such.

as. to. 1eav e;6,% tree. sulnhurio acid.. Ripenine is conducted at. 50 and after about; 6. hours without agitation. at 30 C; until.' the desiredacetyl Valueis reached. 'fFor example, forl an acetyli Value of about 54.5%, this may take'some 50 hours. The resulting celluloseI acetate, whichis then precipitated and Washed', has a higilrvscovs-4 ity of'v the. order of 50:60'. on the scale mentioned above, ygood `clarity and.Y a low contentv of' combined sulphuric. acid. Example H This ililusttates the of alovierdualetite of. watec and a loi-.ieee period ei: einen-.- natoqobtain a product of. medium uisoosity.. acetylation is.n carried out: as in Example.. I, and

wete-a and magnesium carbonate-added., Iheamountoctmaeiiesiuia oatbodatefis the.- same as.l inEXampleLhut theamount est Water fol; ripari-. ing; is on. the oreiualweiehtof the.l cotton... Riceairie' is.. conducted. atifif" 0;. iorf about; d5. hours. The croduethas ay medium. viscosity. a. goed clarity and af. still lower. odatent.of..` combined sulplauric acid-v Y Examplierl Acetylation is carried. out asin Example I and magnesium, carbonate and *waterv added for 'ripv ening. The amount of'magnesi-urn carbonate is such as to leave 2% of -free sulphuric acidi and" a product et. fili-54%', acetyl' value is Produced of lowcombined s ulnhuric acid coment,l goed clarity andmediumviseosity Biff neutralizing, but 4%. of 'thefree sul.-v

phuric acid andconducting the ripening at 60 C.. theriueuine time, maybe. reduced to about 4 hours... While .thefsame ripening time mail be used if. the. ireeaulphuric. acid, is reduced. tolfia.y and. the ripening temperature. raised 130,70". C.. In this last case 'a product of verylow combined, sulphuric acid content, is, obtaided- Ecc@mapleA i/ELI 1.7.0 parte offcotton, arefacetylated 6.3.0. parts. ofaoetic. acid, 3.5.8y :carts of acetic. anhydride and 2.3.5 parte. oisulphuric. acid, the. parte' being by. Weight. The time of acetylation is, 4 .1.5

hours during which. thenuxture' is. allowed, tor

attain appeal; temperature, 0F42?" CI. Water is.

weight of the cotton., Einem-ng ricconduc-ted* at cosityof the same! order as inExarmaleIA);l of.

then added in. amount, only `s uiiicient.to. react with any `free'. acetic anhydride.. Next there. is. addedv to. the acetylation mixture an amount. of; magnesium carbonate sutiioie'nt to. adinet the. suinhurio acid. content to.. an. amo-uut,

equal to.. about. 5.%. off tlie.V Weight of thecell'uiose 'employed/as. the starting material. There isi...

then. added` Water ign-amount-equa-l to 'diie-5.9%

oithe weight oithe cellulose used. order to.

brine about ripening.. Tice-mass. is. agitated-.id

aiacketed WemerePleiderer, machine where its. temperaturen. mai,attainedA at-dof After 2 hours. of'tiiis treatment.. the cellulose acetate. precipitated, hy. vthe `aiditioli oi a, La reev amount o f. water. and. is tiienfwashedgaud dried. The

cellulose acetate hasanaeetyl' value of eti-59%;

calculated'. as acetic acid.V and is( quite solubllein acetone.A `lf the time oiripeni-ngl is extended 'K'co 6- hours, an acetone-comble cellulose acetate rof- 54-55-% acetyl valueisA produced. y N v i The resulting; celluloseacetate 'is orfhigh vis cos/ity: If-thel sameconditionSV-areemployed iiithftlieL exception' .that tltxeV quantityoliiE WaterL added for ripening i`s decreased to about 36% of the weight of the cellulose employedv as' starting material, the celluloseacetate produced is of lower viscosity. ,Y

Example VII I 170 parts of cotton linters are acetylated with an A acetylation solution containingV about 600 parts of acetic acid, 400 parts vof acetica-nhy"- dride and 18 parts of sulphuric acid, all by weight. The time of acetylation is about 11/2 hours during which time the temperature is not allowed to exceed about40 C., On completion of acetylation, water is added' in'an, amount just suiiicient to destroy the excessof acetic'anhy dride and part of the sulphuric acid is neutralized by the addition of abcutparts by weight of magnesium carbonate so as to reducethe sulphuric acid content to` about '1% on the weight of the cellulose employed. 11,0 parts by' weight of'waterare also introduced. The mixture is then well stirred in a jacketed Werner-Pileiderer machine, its temperature being,maintainedk at about 60 C. After about 3'-5 hours treatment, a 35% aqueous solution of acetic acidcontaining about 240 parts by weightof water isadded and the mixture is againstirred for about 1-2 hours at 60 C. Theripened cellulose acetate is'then precipitated by thel addition of a large quantity of water, after which it isV washed and. dried. .It has anfacetyl value of`,.about.54jor 55% and is soluble njacetone. l`The ripening operation may be continuedfor a longer time if a product having a lower,` acetyl content is required. For example, by continuing the opeation for about 1-2 hours longer, aproduct having an acetyl content of about 53-54% may be obtained.

VIt is to be understood that the foregoing detailed description is given merely by way of il,-` lustration and that many variations `may be made therein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

1. Process for the production of cellulose acetates, which comprises acetylating cellulose with acetic anhydride in a medium containing acetic acid as solvent and lil-15% on theweight of the cellulose of sulphuric acid as catalyst, neutralizing part of the sulphuric acid at `the completion of the acetylation by means of Vmagnesium compound so as to leave less than 8!% of free sulphuric acid, and eiecting ripening.

2. Process for the production of cellulose acetates, which comprises acetylating cellulose with acetic anhydride in a medium containing acetic acid as solvent and lll-15% on the weight of the cellulose of sulphuric acid as catalyst, Yrieutralizing part of the sulphurc acid at'the completion of the acetylation by means of a magnesium salt of a weak acid so as to leave less than 8% of free sulphuric acid, and eiiecting ripening.

3. Process for the production of cellulose ace. tates, which comprises acetylating cellulose by means of acetic anhydride in a medium contain` ing acetic acid as solvent and 10-l5% on the weight of the cellulose of sulphuric acid as catalyst, neutralizing part of the `sulphuric acid by means of a magnesium compound s o as to leave 4-8% of free sulpliuric acid, and effecting ripening at 50-65" C. by means of water. r

4. Process for. the production of cellulose Aacetates, which 'comprises acetylating cellulose by means of acetic anhydride in a medium containing acetic'acid as solvent audio-'15% `on. the weight of the 'cellulose of sulphuric acid as catalyst, neutralizing part of the sulphuric acid by means of a magnesium compound so as to leave 443% of free sulphuric acid, and effecting ripeningby means of water while agitating thev miX- ture. 7 5. Process according to'claim 4, wherein ripening is eiected at above 50C.

6. Process for the production of cellulose acetates,4 which comprises acetylating cellulose by means of acetic anhydride in a medium containing acetic acid as solvent and lil-15% on the weight of the cellulose of sulphuricacid as catalyst, .neutralizing part of, the sulphuric acid by means of a magnesium compound so as to leave 4-8% of free sulphuric acid, and effecting ripen-f ing of the cellulose acetate by means of water, and precipitating the cellulose acetate when it has become acetone-soluble and still has an acetyl content, calculated as acetic acid, of more than 56%.',

7. Process for the production of cellulose acetates, which` comprises'acetylating cellulose'4 by means of acetic anhydride in a medium'conta'in` ing acetic acid as solvent and 10-15% on the weight ofthe cellulose of sulphuric'acid ascatalyst, neutralizing part of the sulphuric acid by means of a magnesium compound so as to leave less than 8% of free sulphuric acid, and adding water, allowing to ripen for some time, and then adding more water and continuing'the ripening.

8. Process for the production of cellulose acetates, which comprises acetylating cellulose by means of acetic anhydride in a mediumcontaining 'acetic acid as solvent and 10-15% on the weight of the cellulose of sulphuric acid as catalyst, neutralizing part of the sulphuric acid by means of a magnesium compound so as to leave less than 8% of free sulphuric acid,` and adding water', allowing to stand-until some ripeninghas occurred, and then adding more .water and continuing the ripening, the mixture being agitated throughout the ripening treatment. f

9. Process according to claim 8, wherein the' ripening iseffected at above 50 C.

10. `Process for the production of cellulose ace tate, which comprises acetylating cellulose with acetic acid anhydride in acetic acid as solvent for the cellulose acetate produced, employing from 8 to 15%, based on the weight of the cellulose employed as starting material, of sulphuric acid as catalyst, adjusting the amount of freesulphuric acid present in the primary solution to 4-9% based on theweight of cellulose employed as starting material by means of a compound selected from the group consisting of magnesium andzinc compounds, adding'an amount of water` sucient to convert any acetic` acid anhydride present in the primary solution to acetic acid and an additional amount of water equal to `from l5-40% based on the original weight of the cellulose, and permitting the solution to hydrolyze or ripen at a temperature of I.l0-455 C. until cellulose acetate of the desired characteristics is obtained.

ll. `Process for the productionof cellulose-acetate, which comprises acetylatingcellulose with 1 aceticacid anhydride inacetic acid as solvent for thefcellulose .acetate produced, employing from 8 to 15%, based on the weight of `the cellulose employed as Astarting material, of sulphuric acid as rcatalyst,VA adding magnesium acetate to the primary solution to reduce the amount ofi free `incorporating water with the acetylation soltion sulphuric acid present in the primary solution to 4V-9%' 'based on'the Weight of cellulose employed as startingv material and an amount Vofwvater vsuii'icient to convert any acetic acid anhydride 'presentin the primary solution to acetic acid,

adding an additional amount of water equal to from V-40% based on the. original Weightv of the cellulose, and permittingv the solutionto hydrolyze or ripen at a temperature of Llll-65C;until cellulose acetate of .thefdesired characteristics is obtained.A l y 12. Process for the production of cellulose acetate, which comprises acetylatingcellulose with acetic acid. anhydride in acetic' acidas solvent lfor the'cellulose acetate producedeinploying l2-15%, basedy on the weight of thefcellulos'e employed as 'starting' material, of sulphurie acid as catalyst, addingY to the primary solution magnesiiniiacetate in an amount sullcient tol neutralize'sulstan'- tially' half of the .sulphuric acid present in Said primarysolution,'adding anamount of Water suiiicient to. iconvert' any' .l acetic acid anhydride present inl the-primarysoliition.to acetic acid and an additional. amountoi water equalitow-from .20-30%,basedlon theoriginal-Weight of the cellu lose, permittingathe solution to hydrolyze or ripen ata temperature 'of Lio-60'o 'Cx for at'most ve -l1ours,xand then precipitating the' ripenedcelluloseacetatei J 1 s i Y 13; A method for. the production ofcellulose esters of: lower aliphatic acids,- W'hicl'i comprises esterifying cellulose with an anhydride of a. lower aliphatic acidirra solvent.fortlfie cellulose Aester produced using sulphuric acid-ascatalyst; adjusting the sulphuric; acid. present in tire' primary esteriication.4 solution to la concentration of approximately e. to .8% ,or based on` the viis/"eight 'ofl the cellulose originally present', by means of al compoundaselected from; the groupy consisting of magnesium. and.k zinc :compounds incorporating Waterwth the esterication solution aiidripeningtheester atta; temperature loetwee'rlid 50 and 90? C..Withaagitationffurther water. being incorporated during. ripening an, amountsufcient to bring tliefconcentration-of the sulplinric acid in` Water.. below .that existingat the beginning of tliefripeningroperatonf i y la. A. method for. .ithelproduction oicellulose acetate, which. comprises", l acetylating` cellulose Withxa'cetic :anhydride inaoetic acid vas solvent for tlrecellulose acetate -usingsullohuric acid as catalysttl adjusting. thecsulphu-r-ic acid present inthe prnnaryaacetylation. solution toV aconcentration ofrapproxirnately 4 to-8 baseden-thef weight of the' cellulose originally presen-t,- by 'means of a compound selected from the-groupl consisting of magnesium and zincwcompounds; incorporating water thev acetylations solution and ripening the cellulose.` acetate atA a' 'temperature between v50iandtQfl? C; with agitation;- further Water being incorporated-'duringripeningin anamount suif'- `cientxto bring the concentration -of the rsulplo'urc acid irtwater below that yexistir-laat''the beginning of-ltheripeningtoperation. I .1v

. -15r4 .Ai-methodfor the prodtiction' of cellulose acetate, .':Which comprises acetylating-*cellillose with acetic anhydrideV inacetic-aci" asfls'olvent for the cellulose :acetate .usi-ngi acid: as catalystradj .the ysiilpliurli-cacid` present in .thefprixnary acetylation solutionto 2a/concentration.J of.-.app11oximatelyl4 -tov8f%,- based? onl the -Weiehtnofwthei cellulose originally-present; by means otau compoundl selected the group consisting.'oimaenesiurriardzre compounds,

and Vripening the celluloseacetate at a temperaturey about 60 C. with"agitatior'i,A 'further' Water being incorporated during ripen'iginaiamount .suilicient tobring the'concentration ofthe sulvpliuric acid; in Water'fbelowthat ekistingat thev Vbeginning of the ripenin'gi operationg;

16J A "method lor. ther productionV of vckf-:llulose acetate; which comprises acetylating cellulose withv acetic anhydride in aceticza'cid as solvetfor the cellulose acetate usingsulphuricacid as catalyst, adjusting thesulphuric acid presentin` the primary acetylation solutin'to.aaconcentration 1. goin/retina crimenes l acetate, which .comprisesfagitating-iaisol vof. approximatelygll to 8%, based' ontheiweiglit of thecellulosez'orig'inallyr present, by Ymeans of a compound selected from thev groupconsist-ng. of 'magnesium .and Zinc compounds, V.incorpoating .Water zwithlthe' acetylation .solutionv and; ripening .the cellulose acetateV at a temperature between :'50

and: l C. Withlag'itatgion",v and a'fterl 3. to 5'.hours from the beginning of the ripening incorporating further Water ansiamoun't sumcient: ltd Abring vthe concentration oi; the sulphuric` acid'.y in W'ater vlccloyirtl'iat existing at the beginning of tloer'ipen'-A ing`4 operation.

i r1. Af methcasfcr webredactie@,ofeuuiose' .acetatel which comprises' acetylating. cellulose n Withacetie ahhydride'ir'i acetic acidas s'lventf'or the cellulose .acetateusingsulphuric' acid a'scata- `lySlt.. adjusting .theslph'lrrlc acid :present ini the primary: acetylation solution to fa?. concentration of approximately 4 to 8%, based on thewightof theK cellulose .originally present, .by VzmeaiisA o'f aA '-,co'mp'onhd selected from?thefgroupconsistirig of magnesium: and zinc compounds; :incorporating Ao!aterWiththe acetylationsoluti'on .and ripening the cellulose acetate at 'aE teniperat'ureiaboutf 60 C.

beginning: `of:l the ripening incorporating? .further water inan.- amountafsucient:to-,bring the concentration Aof the :sulplmricV acidin` Water below that existing :ata the beginningy .ofi the ripening .operationiA 18. Method ofnochmariccioli/amg lower fattyl jacidesters of; cellulose, l'whilch com-prises agitatin'ga agsol-u'tion cfa' lower fatty-aci'dfeste'r'; of

cellulose containing ajproportioirV of hydrolyzing catalyst equivaler-itv to .4;ito18% of .sulphurc`acid,

19. Method of ripening orrnycroly' tweliatty: acid' esters .ofv cellulose',` .whi'ciccomprilses agitatingla solutiorrrof aflower `-faitty acidi ester' ofy proportio of Waterislcieri't toeiefct substantial hydrl such cellulose, at a temperaturezof 55 to 75 C.

throughout the period oi hydrolysis and precipitating the cellulose` acetatewhen it has an acetyl .value of 56fto 59%.

21. Process for the manufacture of lower fatty acid esters of cellulose, which comprises ripening or hydrolyzing the lower fatty acid ester of cellulose while in the primary. solution in which it is -formed and which contains magnesium sulphate,

.sulphuric acid in amount of 4 to 8 parts and water in amount of .6 to parts, the parts being` by Weight per 100 parts by weight of cellulose used as the starting material.

22. Process for the manufacture of cellulose acetate, which comprises ripening or hydrolyzing cellulose acetate while in the primary solution in which it is formedl andv which contains magnesium sulphate, sulphuric acid in amount of 4 toS parts and water in amount of v6 to 20` parts, the partsbeing by weight per 100 parts by weight `of cellulose used as the vstarting material.

and interrupting the ripening or hydrolysis before the acetyl value of the cellulose acetate` falls below 57%.

24. Process for the manufacture of cellulose acetate, which comprises ripening or hydrolyzing cellulose acetate while in the primary solution in which it is formed and which contains magnesium sulphate, sulphuric acid in amount of 4 to 8 parts and water in amount of 18 to 19 parts, the parts being by `weight per 100 parts by weight of cellulose used as the starting material.

25. Process for theproduction of cellulose acetate of high acetyl Value,comprising ripening or hydrolyzing the cellulose acetate while in solution in acetic acid containing magnesium sulphate, sulphuric acid in amount of from 4 to 8% and water in amount of 6 to 20% of the cellulose used 'as starting material and interrupting the hy drolysis Abefore the acetyl value of the cellulose acetate falls below 57%.

26. Process orthe productionof cellulose acetate of high acetyl Value, comprising ripening or liydrolyzing the cellulose acetate while in solution in acetic. acidV containing magnesium sulphate, sulphuric acid in amount of 5% and water in amount of about 18-19% of the cellulose used as starting material. i

27. Process for the production of cellulose acetate of high acetyl value, comprising ripening or hydrolyzing the` cellulosef acetate while insolution inracetic acid lcontaining ,magnesium sulphate, sulphuric acid in amount of 5% and water in amount of` about lil-19% of the cellulose used. as starting material and interrupting the hy- Vdrolysisbefore the acetyl Value of the cellulose acetate falls below 57%. l.. i

28. Process for the production of cellulose acetate of high acetyl value,.comprising ripening or hydrolyzing the celulose acetate while in solution in acetic acid ,containing magnesiumsulphate in amount of, 8 to f13%, sulphuric acidin amount of 4. to 8% and. water in amount. of. 46 to 20% of the cellulose used Vas startingmaterial and interrupting the hydrolysis before .the acetyl value of the cellulose acetatefalls below 57%.

CII

29.' Process for the production of cellulose acetate of high acetyl Value, comprising ripening or hydrolyzing the cellulose acetate while 4insolution in acetic acid containing magnesium sulphate in amount of 8 toV 13%, sulphuric acid in amount of 5% .and water in amount of about lis-19% ofthe cellulose used asstarting material and interrupting the hydrolysis before theacetyl value of the cellulose acetate falls below 57%.

30. Process for the production of cellulose acetate, comprising acetylating cellulose` with an acetylating mixture comprising acetic anhydride, acetic acid and sulphuric acid in amount from 9 to 15% of the `weight of the cellulose, and then causing the same to ripen by the additionthereto of a magnesium compound adapted `to neutralize the sulphuricacid under the conditions obtaining ,in restricted amount to leave 4 to 8% of free sulphuric acid andwater in amount of 6 to 20% of the cellulose used as startingmaterial.

31.Y Process for the production of cellulose acetate, ycomprising acetylating cellulose with an acetylating mixture comprising acetic anhydride, acetic acid and sulphuric .acidinamount from 9 to 15 %A of the'weight of the cellu1oseand then Acausing the same to ripenby theaddition thereto of a magnesium compound adapted to neutralize the sulphuric acid underthe conditions obtaining in restricted amount to leave 5% of free sulphuric acid and Water in amount of about 18-19% of thecellulose used aslstarting material. l, a 32. Process for the production ofj cellulose 'acetate, comprising acetylating cellulose, with an acetylating mixture comprising acetic anhydride, acetic acid and sulphuric acid in amountfrom 9 t0 15% of the weight of the cellulose, and then causing the same to ripen by the addition theretooi a magnesium compound adapted to neutralize the sulphuric acid under Ythe conditions ol'itaining` in restricted amount to leave about 5% offree sulphuric acid and water in amount of about l819% of the cellulose used as `starting material .and interrupting the ripening beforethe'acetyl .value of the cellulose acetate I'alls below 57 Process for the production of` ripened cellulose esters, which comprises esterifyingcellulose by means of a lower fatty acid anhydride, using as esteriication-catalyst,irom 9 to 15% of a polybasic inorganic acid selected from thegroup Consisting of sulphuric and phosphoric acids, there arterneutralizing part or' the catalyst by. means of a compound selected from the group'consisting vof magnesium and Yzinc compouridsr and ripening thecellulose esterin the batlrprociuceu which contains a smaller amount of the I'ree polybasic inorganicA acid catalyst.

. `34.`Proces s forV the production of ripenedcellulose esters, which comprises esterifyingcellulose by `means VofV a lower rattyacid anhydride, usinf as esterication catalyst fron119 Ato 15% of sultphuricracid, thereafter neutralizing part of the catalyst by means or' a compound; selectedlrom the group consisting of magnesium and zinc coinpounds, and ripening thecelluloselesterin the bath produced which ,contains Aa Smalleramount of the sulphuriclacid catalyst. i Ln s 35. Process for the production otce'llulose4 acetates, which comprises acetylatingcellulose by means` of acetic anhydride, usingasi acetylation `Catalyst from 9, 1.15% on-.theweight ofthe cellulose of sulphuric acid, so `that the cellulose acetate is produced in;solutionneutralizing part or" the sulphurie acid -at the completion' of the acetylation by means of a compound selected from the group consisting of magnesium and zinc compounds, so as to leave less than 8% of free sulphuric acid, and eiecting ripening in the bath so produced.

36. Process for the production of cellulose ace-y tates, which comprises acetylating cellulose by means of acetic anhydride in presence of acetic acid as solvent, using as acetylation catalyst 10 to 15% on the Weight of the cellulose of sulphuric acid, neutralizing part of the sulphuric acid at the completion of the acetylation by means of a compound selected from the group consisting of magnesium and zinc compounds, so as to leave less than 8% of free sulphuric acid, and effecting ripening in the bath so produced.

37. Process for the production of cellulose acetates, which comprises acetylating cellulose by means of acetic anhydride in presence of acetic v 

